[time-nuts] 5>10 doubler

[Charles Steinmetz]

Bill wrote:

>Push-Push Jfet amplifier with parallel inputs and a Toroid output 
>transformer, no secondary along with a simple filter using a 10 MHz 
>series resonate crystal connected to one drain and an adjustable 
>capacitor connected to the other would work fine. You connect the 
>other ends of the two together and a loading resistor to 
>ground.  The capacitor is used to neutralize or null out the shunt 
>capacitance of the crystal so that a capacitive path for the other 
>frequencies , 5, 15, 20, etc is eliminated.

I concur with what Bruce said regarding crystal filters (or any 
narrow bandpass filter) at the output frequency.

More fundamentally, I'm not sure I understand your description of the 
circuit.  You say it is a pair of FETs with parallel input and a 
transformer (autoformer) output.  To me, that suggests the circuit 
pictured below (one feeds the sources in parallel, the other feeds 
the gates in parallel -- it doesn't make any difference in how the 
circuit operates).

The usual push-push doubler feeds the FETs differentially, and takes 
the common-mode output.  The diagrammed circuit reverses this -- it 
feeds the FETs in parallel (common-mode) and takes the 10MHz output 
differentially.  As drawn, the circuit would have essentially no 
output at the input frequency or any of its harmonics (only that due 
to the mismatch between the FETs).  The only signals it would amplify 
are uncorrelated signals -- i.e., the FETs' input noise voltages.  A 
quick simulation confirmed no significant output at the input 
frequency or its harmonics for matched FETs.  Simulating mismatched 
FETs produced a 5MHz signal rich in harmonics, but at a very low 
level and with no suppression of the 5MHz and its odd harmonics.

I assume I misinterpreted your description and that you had a 
different circuit in mind, or that if you did have this circuit in 
mind I'm missing something about its operation.  Can you please 
describe again what you had in mind, and how it generates 10MHz?

Best regards,

Charles

-------------- next part --------------
A non-text attachment was scrubbed...
Name: Fuqua_doubler_sm.gif
Type: image/gif
Size: 17911 bytes
Desc: not available
URL: <http://febo.com/pipermail/time-nuts_lists.febo.com/attachments/20150204/ed4fa496/attachment.gif>